Moisture barrier film

ABSTRACT

A multiple layer film useful in moisture barrier packaging applications has at least one layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two additional layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof. A core layer of ethylene vinyl alcohol copolymer or other oxygen barrier material, or high density polyethylene, can be included in some embodiments. A preferred embodiment of the multi-layer film exhibits excellent moisture barrier and optical properties, and shrink properties as well if the film has been oriented. High oxygen barrier is also a feature in embodiments including EVOH or other oxygen barrier materials.

This is a Divisional application of application Ser. No. 08/358,121,filed Dec. 16, 1994 U.S. Pat. No. 5,543,223, which is a Divisionalapplication of application Ser. No. 08/116,798 filed Sep. 10, 1993 U.S.Pat. No. 5,482,771, which is a Continuation-In-Part of application Ser.No. 07/947,244 filed Sep. 18, 1992 abandoned.

FIELD OF THE INVENTION

This invention relates to thermoplastic films for packaging; and moreparticularly, this invention relates to a multi-layer film having highmoisture barrier characteristics.

BACKGROUND OF THE INVENTION

Thermoplastic film, and in particular polyolefin materials, have beenused for some time in connection with packaging of various articlesincluding food products which require protection from the environment,an attractive appearance, and resistance to abuse caring the storage anddistribution cycle. Suitable optical properties are also desirable inorder to provide for inspection of the packaged product after packaging,in the distribution chain, and ultimately at point of sale. Opticalproperties such as high gloss, high clarity, and low hazecharacteristics contribute to an aesthetically attractive packagingmaterial and packaged product to enhance the consumer appeal of theproduct.

Various polymeric materials have been used to provide lower moisturepermeability in order to reduce the transmission of moisture through thepackaging film and thereby extend the shelf life of products such asfood, medical, electronic, and other items which are sensitive tomoisture gain or loss. For some products, maintenance of a high moisturecontent is desirable, and the film ideally minimizes loss of moisturefrom the package to the environment. For other products, maintenance ofa low moisture content is desirable, and the film ideally minimizes gainof moisture from the environment through the packaging material.

It is also often desirable to include in a packaging film a shrinkfeature, i.e, the propensity of the film upon exposure to heat to shrinkor, if restrained, create shrink tension within the packaging film. Thisproperty is imparted to the film by orientation of the film during itsmanufacture. Typically, the manufactured film is heated to itsorientation temperature and stretched in either a longitudinal (machine)or transverse direction (i.e. monoaxial orientation), or both directions(i.e. biaxial orientation), in varying degrees to impart a certaindegree of shrinkability in the film upon subsequent heating. Whenbiaxial orientation is done, it can be simultaneous or sequential; thatis, the orientation can be done in each of the directions in turn, orelse both the longitudinal and transverse orientation can be done at thesame time. Any suitable technique, such as blown bubble ortenterframing, can be used to achieve orientation of the film. Afterbeing so stretched, the film is rapidly cooled to provide this latentshrinkability to the resulting film. One advantage of shrinkable film isthe tight, smooth appearance of the wrapped product that results,providing an aesthetic package as well as protecting the packagedproduct from environmental abuse. Various food and non-food items may beand have been packaged in shrinkable films.

It is sometimes also desirable to orient a packaging film and thereafterheat set the film by bringing the film to a temperature near itsorientation temperature. This produces a film with substantially lessshrinkability, while retaining much of the advantages of orientation,including improved tensile strength, modulus and optical properties.

It is an object of the present invention to provide a thermoplasticmultilayer film characterized by good moisture barrier properties.

It is a further object of the present invention to provide athermoplastic multilayer film having an aesthetic appearance with goodclarity, and other desirable optical properties.

It is another object of the present invention to provide a thinthermoplastic multilayer film having toughness and abrasion resistance.

It is still another object of the present invention to provide athermoplastic multilayer film which may be totally coextruded, oriented,and have good moisture barrier and, in some cases, both moisture barrierand oxygen barrier properties.

Of interest are U.S. Pat. No. 4,921,749 (Bossaert et al); U.S. Pat. No.5,085,943 (Crighten et al); U.S. Pat. No. 5,091,237 (Schloegel et al);U.S. Pat. No. 5,128,183 (Buzio); and U.S. Pat. No. 5,212,009 (Peiffer etal) disclosing the use of hydrocarbon resins.

SUMMARY OF THE INVENTION

The present invention relates to a thermoplastic multi-layer filmcomprising a core layer comprising a blend of propylene polymer orcopolymer, or ethylene alpha olefin copolymer, and a hydrocarbon resin;and two outer layers comprising a propylene polymer or copolymer,ethylene alpha olefin copolymer, polybutene, or blends thereof.

In another aspect, the present invention relates to a thermoplasticmulti-layer film comprising a core layer comprising a blend of propylenepolymer or copolymer, and a hydrocarbon resin; two intermediate layers,on opposite surfaces of the core layer, comprising propylene polymer orcopolymer, or a polymeric adhesive; and two outer layers comprising apropylene polymer or copolymer, ethylene alpha olefin copolymer,ionomer, polybutene, or blends thereof.

The present invention also relates to a thermoplastic multi-layer filmcomprising a core layer comprising an ethylene alpha olefin copolymer,ethylene propylene copolymer, rubber modified ethylene propylenecopolymer, or ethyene propylene butane terpolymer; two intermediatelayers, on opposite surfaces of the core layer, comprising a blend ofpropylene polymer or copolymer, and a hydrocarbon resin; and two outerlayers comprising a propylene polymer or copolymer, ethylene alphaolefin copolymer, ionomer, polybutene, or blends thereof.

A film with oxygen barrier as well as moisture barrier propertiescomprises a core layer comprising an oxygen barrier material; twointermediate layers, on opposite surfaces of the core layer, comprisinga polymeric adhesive; two outer layers comprising a blend of propylenepolymer or copolymer, or polybutene, and a hydrocarbon resin; and apolymeric sealant layer adhered to at least one of the outer layers.

An alternative film with at least seven layers comprises a core layercomprising high density polyethylene; two intermediate layers, onopposite surfaces of the core layer, comprising a polymeric adhesive,ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer;two outer layers comprising a blend of propylene polymer or copolymer,and a hydrocarbon resin; and two outermost layers comprising propylenepolymer or copolymer, polybutene, or blends thereof.

Another alternative is a film comprising a core layer comprising anoxygen barrier material; two intermediate layers, on opposite surfacesof the core layer, comprising polyamide; two tie layers, each disposedon a respective polyamide layer, comprising a polymeric adhesive,ethylene alpha olefin copolymer, or ethylene vinyl acetate copolymer;two moisture barrier layers, adhered to respective adhesive layers,comprising a blend of propylene polymer or copolymer, and a hydrocarbonresin; and two outermost layers comprising a propylene polymer,propylene copolymer, ethylene alpha olefin copolymer, or polybutene.

In another aspect of the invention, a method of making a thermoplasticmultilayer film comprises the steps of coextruding an interior layer ofa blend of propylene polymer or copolymer, and a hydrocarbon resin, andtwo outer layers comprising a propylene polymer or copolymer, ethylenealpha olefin copolymer, polybutene, or blends thereof; cooling thecoextruded multilayer film; and collapsing the cooled film.

DEFINITIONS

“Hydrocarbon resin” (“HC” herein) and the like as used herein meansresins made by the polymerization of monomers imposed of carbon andhydrogen only. Thermoplastic resins of low molecular weight made fromrelatively impure monomers derived from coal-tar fractions, petroleumdistillates, etc. are also included. A discussion of HC resins can befound e.g. in U.S. Pat. No. 4,921,749 (Bossaert et al); U.S. Pat. No.5,091,237 (Schloegel et al); and U.S. Pat. No. 5,128,183 (Buzio).

“Ethylene alpha olefin copolymer” (EAO) is used here to include suchmaterials as linear low density polyethylene (LLDPE); very low and ultralow density polyethylene (VLDPE and ULDPE); and metallocene catalyzedpolymers such as those supplied by Exxon. Tafmer (tm) materials suppliedby Mitsui are also included. These materials generally includecopolymers of ethylene with one or more comonomers selected from C₄ toC₂₀ alphaolefins such as butene-1, hexene-1, octene-1, etc. in which themolecules of the copolymers comprise long chains with relatively fewside chain branches or cross-linked structures. This molecular structureis to be contrasted with conventional low or medium densitypolyethylenes which are more highly branched than their respectivecounterparts. “LLDPE” as defined here has a density in the range of fromabout 0.916 grams per cubic centimeter to about 0.940 grams per cubiccentimeter. Generally, “EAO” as used here includes both homogeneous andheterogeneous polymers. “Intermediate layer” and the like is used hereinto define a layer in a multi-layer film enclosed on both sides by otherlayers, i.e. disposed between other layers of the film.

The term “oriented” and the like is used herein to define a polymericmaterial in which the molecules have been aligned in the longitudinaland/or transverse direction by a process such as a tenter frame or blownbubble process.

“Propylene polymer” and the like is used here to mean polymerizedpropylene in its homopolymer form, and “propylene copolymers” meanscopolymers such as ethyene propylene copolymer, where generally smallamounts of a comonomer such as ethylene are included in the copolymer.Terpolymers are also included.

“Polymeric adhesive” and the like here means polymeric materials, of anysuitable composition, which can be used to create or enhanceinterlaminar bonds in multilayer thermoplastic films. Polyolefins arepreferred, especially those which have been modified, e.g. by carboxylicacid or acid anhydride in a graft copolymer.

“Rubber modified as EPC” and the like here means an EPC which has beenmodified by the inclusion of other moieties in the polymer structure.Such material may provide improved elasticity or other properties. Anexample is believed to be Himont KS-052 P, or those available fromRexene (El Paso).

“Ethylene propylene butene terpolymer” and the like is used here to meana terpolymer incorporating these three comonomers in variouspercentages. An example is KT-021 from Himont, or those available fromSumitomo.

“Core layer” as used herein means an intermediate layer of a multilayerfilm, and the central layer where the film has an odd number of layers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details are given below with reference to the drawing figureswherein

FIG. 1 is a schematic cross section of a preferred embodiment of amulti-layer moisture barrier film of the invention, and

FIGS. 2 and 3 are alternative embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring specifically to the drawings, in FIG. 1, a schematic crosssection of a preferred embodiment of the multi-layer moisture barrierfilm of the invention is shown. The multi-layer film 10 has thegeneralized structure of A/B/A where A is an outer layer, and B is acore layer comprising a moisture barrier material.

Core layer 12 preferably comprises a blend of a propylene polymer orcopolymer, and a hydrocarbon resin, this blend shown as aspotted/striped layer. A typical example of a propylene homopolymer isExxon PD 4062 E7, or those available from Fina, or Himont PD 064. Apreferred propylene copolymer is ethylene propylene copolymer sold underthe designation Fina 8473 or Fina 8473X. This material has an ethylenecontent of about 4%. A preferred hydrocarbon resin is Regalrez 1128 or1139 from Hercules. The HC resin preferably comprises between about 30%and 50% by weight of the blend.

Outer layers 14 and 16 are preferably ethylene propylene copolymer(EPC), polypropylene (PP), or blends thereof. If only polypropyleneresin is used, the film can be difficult to use for packagingapplications involving heat sealing. Therefore, it is preferable to useEPC alone, or the blend of the two materials. Commercial resin examplesare those discussed above for core layer 12. An alternativepolypropylene for the outer layers 14 and 16 is Himont PDO 64. Theseblend layers may include from 0-100% EPC and 100%-0% PP, althoughpreferably the blend layers include between about 96% and 85% EPC andbetween about 4% and 15% PP; even more preferably, the blend layerincludes about 92% EPC and 8% PP. EAO and polybutene can also be used inthe outer layers.

In FIG. 2, a schematic cross section of another embodiment of themulti-layer moisture barrier film of the invention is generally shown.The multi-layer film has the structure of A/B/C/B/A where A is an outerlayer, B is an intermediate adhesive layer, and C is a core layercomprising a moisture barrier material.

The core layer preferably comprises a blend of a propylene polymer orcopolymer, and a hydrocarbon resin. Suitable materials are thosedescribed above for core layer 12 of film 10.

The outer layers are preferably the materials discussed above for outerlayers 14 and 16 of film 10. The outer layers also preferably include anHC such as described for core layer 12 of film 10.

The intermediate layers preferably comprise a propylene polymer orcopolymer, or blends thereof, optionally blended with hydrocarbon resin.

An alternative A/B/C/B/A structure is also within the scope of thisinvention, and specifically shown by the position of the moisturebarrier layers in the film of FIG. 2.

In this alternative, core layer 24 preferably comprises an ethylenealpha olefin copolymer, more preferably a linear EAO. Very low densitypolyethylene (VLDPE), and linear low density polyethyene (LLDPE) arepreferred. A suitable LLDPE is Dowlex 2045. The core layer 24 can alsocomprise EPC, a rubber modified EPC, or an ethylene terpolymer,especially an ethylene propylene butene terpolymer such as KT 021 P fromHimont.

Outer layers 20 and 28 are preferably the materials discussed above forouter layers 14 and 16 of film 10.

Intermediate layers 22 and 26 preferably comprise a blend of a propylenepolymer or copolymer, and a hydrocarbon resin. Suitable materials arethose described above for core layer 12 of film 10. An alternativematerial for layers 22 and 26 is Exxon 6042, which is believed to be ablend of polypropylene and hydrocarbon resin.

In FIG. 3, a schematic cross section of another embodiment of themulti-layer moisture barrier film of the invention is shown. Themulti-layer film 30 has the generalized structure of A/B/C/D/C/B/A whereA is an outer layer, B is a moisture barrier layer, C is an intermediateadhesive layer, and D is a core layer comprising an oxygen barriermaterial.

Core layer 38 preferably comprises an oxygen barrier material such asethylene vinyl alcohol copolymer, vinylidene chloride copolymer,polyester, or polyamide.

Outer layers 32 and 44 are preferably the materials discussed above forouter layers 14 and 16 of film 10.

Intermediate layers 36 and 40 preferably comprise a propylene polymer orcopolymer, such as Exxon PD 4062 E7. Alternative materials are polymericadhesives, especially carboxylic acid or maleic anhydride-modifiedpolyolefins and more preferably polypropylene-based carboxylic acid ormaleic anhydride-modified adhesives. Conventional lamination or othersuitable methods may sometimes be necessary, depending on the nature ofthe respective layers, to ensure adequate interlaminar bond strength.

Moisture barrier layers 34 and 42 preferably comprise a blend of apropylene polymer or copolymer, and a hydrocarbon resin. Suitablematerials are those described above for core layer 12 of film 10. Analternative material for layers 34 and 42 is Exxon 6042.

An alternative film with at least seven layers comprises a core layer 38comprising high density polyethylene; two intermediate layers 36 and 40,on opposite respective surfaces of the core layer, comprising apolymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alphaolefin copolymer; two moisture barrier layers 34 and 42 comprising ablend of propylene polymer or copolymer and a hydrocarbon resin; and twooutermost layers 32 and 44 comprising propylene polymer or copolymer.

A multilayer film of four or six layers, and/or possessing both moisturebarrier and oxygen barrier properties, can also be made in accordancewith the present invention. In such alternative constructions, a blendof HC resin with propylene polymer or copolymer can be present in any ofthe layers of the multilayer film.

The core, intermediate, and moisture barrier layers of such a film canbe like that of film 30. A sealant layer is coextruded with, orextrusion coated, extrusion laminated, or adhesive laminated, by meansand methods well known in the art, to one of the moisture barrierlayers. The sealant layer, which can be disposed on one or both outersurfaces of the film structure, preferably comprises an ethylene alphaolefin copolymer, more preferably a linear EAO. Very low densitypolyethylene (VLDPE), and linear low density polyethyene (LLDPE) arepreferred. A suitable LLDPE is Dowlex 2045. The sealant Layer can alsocomprise EPC, a rubber modified EPC, an ethylene propylene buteneterpolymer such as KT 021 P from Himont, an ethylene vinyl acetatecopolymer, an ethylene alkyl acrylate copolymer, an ethylene acrylic ormethacrylic acid copolymer, or an ionomer.

The films of the present invention can be made by coextrusion, extrusioncoating, extrusion laminating, and conventional adhesive laminationtechniques well known in the art, using annular or slot die extrusionequipment as appropriate.

The beneficial low moisture transmission rates (high moisture barrier)and other properties associated with exemplary films of the presentinvention are demonstrated in the Tables.

The resins used in these examples are identified in Table 1, and thefilms made from these resins are identified in Tables 2 through 8.

Physical properties of these films are itemized in the remaining Tables.Values given are typically average values obtained from four replicatemeasurements; values for MVTR are average obtained from three samples.

The terms and abbreviations In the Tables have the following meaning:

“PP”=polypropylene.

“EPC”=ethylene propylene copolymer.

“EAC”=ethylene alpha olefin copolymer.

“EPB”=ethylene propylene butene terpolymer.

“EVOH”=ethylene vinyl alcohol copolymer.

“ADH”=polymeric adhesive; ADH 1 is an ethylene butene-based adhesivefrom Du Pont; ADH 2 is an EPC-based adhesive from Mitsui.

“AB”=antiblock.

“MO”=mineral oil.

“Tensile”=tensile at break and 73° F., in PSI (ASTM D 882-81).

“PSI”=pounds per square inch (ASTM 882-81).

“Unshrunk”=a film sample or samples that were not shrunk by exposure toheat at the time of testing for the stated property.

“Shrunk”=a film sample or samples that were shrunk by exposure to heatat the time of testing for the stated property.

“LD”=longitudinal orientation direction.

“TD”=transverse orientation direction.

“Modulus”=modulus of elasticity (ASTM 882-81) in PSI at 73° F.

“Haze”=haze (ASTM D 1003-61 (reapproved 1977)) in percent.

“Clarity”=total light transmission (ASTM D 1003 Method A) in percent.

“Gloss”=gloss measured at 45° angle to film surface (ASTM D 2457-70(reapproved 1977)).

“MVTR 1”=moisture (water) vapor transmission rate (ASTM F 372) ingrams/24 hours, 100 square inches at 100% relative humidity and 100° F.

“MVTR 2”=moisture (water) vapor transmission rate (ASTM F 372) ingrams/24 hours, 100 square inches at 90% relative humidity and 100° F.

“OTR”=oxygen transmission rate (ASTM D 3985-81) in cc at standardtemperature and pressure, in 24 hours, per square meter, at oneatmosphere, at 0% relative humidity.

“Teat”=tear propagation in grams at 73° F. (ASTM D 1938-79).

“Film Thickness”=the average thickness (gauge) of the film samples inmils (=0.001 inches).

“Tensile”=tensile strength at break (ASTM D 882-81) in psi.

“Elongation”=elongation at break (ASTM D 882-81) in percent.

“Ball Burst”=ball burst impact in centimeters-kilograms at 73° F. (ASTMD 3420-80).

TABLE 1 MATERIAL TRADENAME SUPPLIER PP 1 Profax PD-064 Himont PP 2* [seefootnote] PP 3 PD 4062 Exxon PP 4** Escorene PD 6042 Exxon [seefootnote] EPC 1 Fina 8473 or Fina Fina 8473 X EPC 2*** [see footnote]EPC 3 PD 9302 Exxon EPB 1 KT-021 Himont HC 1 Regalrez 1128 Hercules HC 2Escorez 5340 Exxon HC 3 Regalrez 1139 Hercules EAO 1 Dowlex 2045.03 DowEAO 2 Dowlex 2045.04 Dow ADH 1 Bynel CXA 4104 Du Pont ADH 2 Admer QF 551A Mitsui EVOH 1 EVAL SC H-103 Evalca EVOH 2 EVAL LC F-101 A Evalca EVOH3 EVAL LC H-103 Evalca MO 1 Kaydol Witco *PP 2 is a masterbatch blend ofPP 1 with about 4%, by weight of the blend, of a silica-containinganti-blocking agent, about 5% by weight of amide waxes, and about 1% ofa lubricating agent. The amide waxws and lubricating agent are wellknown in the art as slip agents. **PP 4 is Escorene PD 6042, believed tobe a blend of polypropylene and hydrocarbon resin. ***EPC 2 is a blendof EPC 1 blended with about 1.5%, by weight of the blend, of anantiblock agent, and 0.5%, by weight of the blend, of a mineral oil.

TABLE 2 (CONTROL)

Initial efforts to make a moisture carrier material involved the use ofhomopolymer polypropylene in a core layer, with sealant layers ofpropylene copolymer on both surfaces of he core layer. The object was tomaximize thickness of the core layer to minimize the moisture vaportransmission rate (MVTR), while still maintaining adequate free shrinkand sealability properties of the film. The MVTR did not prove adequatefor at least some moisture barrier packaging applications. An example ofthis film is given below:

EXAMPLE FILM STRUCTURE 1. 92% EPC 1 + 8% PP 2/PP 1/92% EPC 1 + 8% PP 2The generalized structure of the film of Example 3 was A/B/A. Relativelayer thickness ratios: A = 1.0; B = 2.0; A = 1.0

TABLE 3

The films of Table 3 were made in an effort to make a moisture barriermaterial with tower MVTR. This was achieved using hydrocarbon resinblended with homopolymer polypropylene. It was found that theseformulations had much lower moisture vapor transmission rate (MVTR) thanthose of Table 2. However, they could not be oriented much over 4.5×4.5racking (orientation) ratio because of equipment limitations. On otherequipment, e.g. a modified bubble process or tenterframing, higherorientation (racking) rates can be achieved. They also could not be madeinto heavier gauge films because of relatively poor tear properties.Examples of these films are given below:

EXAMPLE FILM STRUCTURE 2. 90%[92% EPC 1 + 8% PP 2] + 10% HC 1 PP 3 84.5%PP 3 + 15% HC 1 + 0.5% MO 1 PP 3 90%[92% EPC 1 + 8% PP 2] + 10% HC 1 Thegeneralized structure of the film of Example 2 was A/B/C/B/A. Relativelayer thickness ratios: 2.5:0.8:3.7:0.6:2.4. 3. 92% EPC 1 + 8% PP 2/PP4/92% EPC 1 + 8% PP 2 The generalized structure of the film of Example 3was A/B/A. Relative layer thickness ratios: 1:2:1 4. 92% EPC 1 + 8% PP2/PP 4/92% EPC 1 + 8% PP 2 The generalized structure of the film ofExample 4 was A/B/A. Relative layer thickness ratios: 1:3:1.

TABLE 4

Alternative films of Table 4 were made in which, in effect, the corelayer of the films of Table 3 (i.e. the layer containing the hydrocarbonresin) were “split” into two substrate (intermediate) layers. A “new”core layer of e.g. LLDPE or EPC is introduced. The practical effect ofthis is to improve tear properties of the film, related to tape creasingduring the orientation process, so that it can be oriented at e.g. 6×6ratio. The film was in fact oriented at 4×4.5 because of the equipmentlimitations discussed for the Examples of Table 3. Examples of thesefilms are given below:

EXAMPLE FILM STRUCTURE 5. 92% EPC 1 + 8% PP 2/PP 4/EAO 1/PP 4/92% EPC1 + 8% PP 2 The generalized structure of the film of Example 5 wasA/B/C/B/A. Relative layer thickness ratios: 1.5:3:1:3:1.5. 6. 92% EPC1 + 8% PP 2/PP 4/EPC 1/PP 4/92% EPC 1 + 8% PP 2 The generalizedstructure of the film of Example 6 was A/B/C/B/A. Relative layerthickness ratios: 1.5:3:1:3:1.5

TABLE 5

The inventor took the basic constructions of Table 4, and oriented themat generally higher racking ratios of 6×6. The result was a film showingimprovements in (i.e. lower) MVTR. Examples of these films are givenbelow:

EXAMPLE FILM STRUCTURE 7. 92% EPC 1 + 8% PP 2/PP 4/EAO 1/PP 4/92% EPC1 + 8% PP 2 The generalized structure of the film of Example 7 wasA/B/C/B/A. This film was like that of Example 5, but with both MD and TDracking ratios of about 6 × 6 in the longitudinal and transversedirections respectively. Relative layer thickness ratios: 1.5:3:1:3:1.5.8. 92% EPC 1 + 8% PP 2/PP 4/EAO 1/PP 4/92% EPC 1 + 8% PP 2 Thegeneralized structure of the film of Example 8 was A/B/C/B/A. This filmwas like that of Example 7, but oriented at a higher temperaturecompared to Example 7. Relative layer thickness ratios: 1.5:3:1:3:1.5 9.92% EPC 1 + 8% PP 2/PP 4/EAO 2/PP 4/92% EPC 1 + 8% PP 2 The generalizedstructure of the film of Example 9 was A/B/C/B/A. Relative layerthickness ratios: 1.5:3:1:3:1.5. 10. 92% EPC 1 + 8% PP 2/PP 4/EPB 1/PP4/92% EPC 1 + 8% PP 2 The generalized structure of the film of Example10 was A/B/C/B/A. Relative layer thickness ratios: 1.5:3:1:3:1.5. 11.92% EPC 1 + 8% PP 2 70% PP 3 + 30% HC 2 EAO 2 70% PP 3 + 30% HC 2 92%EPC 1 + 8% PP 2 The generalized structure of the film of Example 11 wasA/B/C/B/A. Relative layer thickness ratios: 1.5:3:1:3:1.5. 12. 90% EPC1 + 10% PP 2/PP 4/EPC 1/PP 4/90% EPC 1 + 10% PP 2 The generalizedstructure of the film of Example 12 was A/B/C/B/A. Relative layerthickness ratios: 1.5:3:1:3:1.5. 13. 90% EPC 1 + 10% PP 2/PP 4/EPC 1/PP4/90% EPC 1 + 10% PP 2 The generalized structure of the film of Example13 was A/B/C/B/A. This film was like that of Example 12, but lowerracking ratios of 4.5 × 4.5 to produce a film of 132 gauge thickness.Relative layer thickness ratios: 1.5:3:1:3:1.5. 14. 90% EPC 1 + 10% PP2/PP 4/EPC 1/PP 4/90% EPC 1 + 10% PP 2 The generalized structure of thefilm of Example 14 was A/B/C/B/A. This film was like that of Example 13,but with slightly higher racking ratios (4.5 × 5.0) and a final filmthickness of 155 gauge. Relative layer thickness ratios: 1.5:3:1:3:1.5.15. 87.5% EPC 3 + 12.5% PP 2 PP 4 EPC 3 PP 4 87.5% EPC 3 + 12.5% PP 2The generalized structure of the film of Example 15 was A/B/C/B/A.Relative layer thickness ratios: 1.5:3:1:3:1.5. 16. 84% EPC 3 + 16% PP 2PP 4 EPC 3 PP 4 84% EPC 3 + 16% PP 2 The generalized structure of thefilm of Example 16 was A/B/C/B/A. Relative layer thickness ratios:1.5:3:1:3:1.5. 17. 86% EPC 3 + 14% PP 2 PP 4 EPC 3 PP 4 86% EPC 3 + 14%PP 2 The generalized structure of the film of Example 17 was A/B/C/B/A.Relative layer thickness ratios: 1.5:3:1:3:1.5.

TABLE 6

The inventor made a seven layer film (Example 18) as a control, and thenmade two moisture/oxygen barrier seven-layer films (Examples 19 and 20)with good results. Examples of these films are given below:

EXAMPLE FILM STRUCTURE 18. 92% EPC 1 + 8% PP 2 PP 3 ADH 2 EVOH 1 ADH 2PP 3 92% EPC 1 + 8% PP 2 The generalized structure of the film ofExample 18 was A/B/C/D/C/B/A. Relative layer thickness ratios:1:2.5:1:1:1:2.5.:1 19. 92% EPC 1 + 8% PP 2 PP 4 ADH 1 EVOH 2 ADH 1 PP 492% EPC 1 + 8% PP 2 The generalized structure of the film of Example 19was A/B/C/D/C/B/A. Relative layer thickness ratios: 1.5:2:1:1:1:2:1.520. 92% EPC 1 + 8% PP 2 PP 4 ADH 2 EVOH 3 ADH 2 PP 4 92% EPC 1 + 8% PP 2The generalized structure of the film of Example 20 was A/B/C/D/C/B/A.Relative layer thickness ratios: 1.5:2:1:1:1:2:1.5

TABLE 7

Two alternative films of seven layers have the structure:

21. 92% EPC 1+ 8% PP 2 PP 4 EVA 1 HDPE 1 EVA 1 PP 4 92% EPC 1 + 8% PP 2The generalized structure of the film of Example 21 is A/B/C/D/C/B/A.Relative layer thickness ratios: 1:2.5:1:1:1:2.5:1 22. 92% EPC 1+ 8% PP2 PP 4 VLDPE 1 HDPE 1 VLDPE 1 PP 4 92% EPC 1 + 8% PP 2 The generalizedstructure of the film of Example 22 is A/B/C/D/C/B/A. Relative layerthickness ratios: 1:2.5:1:1:1:2.5:1

TABLE 8

Two additional alternative films of five layers were made, and arecompared in Table 13 with the film of Example 17. These two additionalfilms have the following structures:

23. 86% EPC 3+ 14% PP 2 PP 4 85% EPC 3+ 15% HC 3 PP 4 86% EPC 3+ 14% PP2 The generalized structure of the film of Example 23 is A/B/C/B/A.Relative layer thickness ratios: 1.5:3:1:3:1.5 24. 86% [85% EPC 3+ 15%HC 3] + 14% PP 2 PP 4 85% EPC 3+ 15% HC 3 PP 4 85% EPC 3+ 15% HC 3 Thegeneralized structure of the film of Example 24 is A/B/C/B/C. Relativelayer thickness ratios: 1.5:3:1:3:1.5

TABLE 9 Example 1 (control) Example 2 Example 3 Example 4 Modulus LD239,480 279,920 316,030 336,820 TD 214,690 260,240 298,930 316,820 FreeShrink/Shrink Tension at 220° F.: LD 7/396 9/321 10/315 11/408 TD 12/38814/381 17/528 17/504 at 220° F.: LD 12/435 14/335 14/361 15/439 TD18/432 19/383 24/540 25/548 at 240° F.: LD 18/451 20/364 20/443 22/494TD 26/469 28/413 33/591 33/516 at 260° F.: LD 31/473 31/397 33/42933/511 TD 35/493 39/441 45/538 44/561 Haze Unshrunk 1.2 1.7 1.3 1.3Shrunk 1.6 2.3 3.2 2.1 Clarity Unshrunk 81 87 87 88 Shrunk 80 84 83 87Gloss 87 84 87 88 Film Thickness (mils) (related to MVTR data givenbelow) Unshrunk 0.96 0.80 0.77 0.75 Actual MVTR 1 Unshrunk 0.60 0.670.60 0.55 Corrected 0.77 0.71 0.62 0.55 for 75 gauge MVTR 2 Unshrunk0.49 0.55 0.48 0.45 Corrected 0.63 0.59 0.49 0.45 for 75 gauge

TABLE 10 Example 7 Example 8 Example 9 Example 10 Modulus LD 271,200299,200 — — TD 292,100 337,900 — — Free Shrink at 220° F.: LD — — 13 13TD — — 19 20 at 240° F.: LD 20 17 20 18 TD 28 23 30 27 at 260° F.: LD —— 27 28 TD — — 37 38 Haze Unshrunk — — 1.7 1.8 Clarity Unshrunk — — 8284 Gloss — — 84 85 Film Thickness (mils) (related to MVTR data givenbelow) Unshrunk 0.86 0.76 0.86 0.77 Shrunk 1.00 0.97 — — MVTR 1 Unshrunk0.51 0.56 — — Shrunk 0.41 0.46 — — Corrected for 75 gauge Unshrunk 0.580.57 — — Shrunk 0.55 0.59 — — MVTR 2 Unshrunk 0.45 0.47 0.42 0.43 Shrunk0.35 0.38 — — Corrected for 75 gauge Unshrunk 0.52 0.48 0.48 0.44 Shrunk0.47 0.49 — — Tear (grams) LD — — 8.6 5.0 TD — — 8.4 6.1

TABLE 11 Example 11 Example 12 Example 13 Example 14 Modulus LD 345,750352,880 322,950 320,470 TD 374,990 392,020 334,660 319,420 Free Shrinkat 240° F.: LD 20 17 18 14 TD 29 23 24 25 Haze Unshrunk 48.5 1.3 3.3 5.3Clarity Unshrunk 21 85 74 64 Gloss 107 89 73 64 Film Thickness (mils)(related to MVTR data given below) Unshrunk 0.85 0.81 1.40 1.60 MVTR 2Unshrunk 0.36 0.36 0.23 0.19 Corrected 0.41 0.39 0.43 0.41 for 75 gaugeTear (grams) LD — — 8.6 5.0 TD — — 8.4 6.1

TABLE 12 Example 19 Example 20 Modulus LD 300,890 307,380 TD 315,460291,480 Free Shrink/Shrink Tension at 220° F.: LD 8/440 14/395 TD 19/63220/595 at 240° F.: LD 18/477 21/439 TD 28/654 27/611 at 260° F.: LD28/446 29/436 TD 38/621 35/601 at 280° F.: LD 44/467 43/487 TD 52/60046/587 at 300° F.: LD 59/— 60/— TD 62/— 61/— Haze Unshrink 1.6 1.8Clarity Unshrunk 76 76 Gloss 89 86 Film Thickness (mils) (related toMVTR data given below) Unshrunk 1.09 1.12 MVTR 2 Non-shrunk 0.35 0.33Corrected 0.51 0.49 for 75 gauge Tear LD 6 6 TD 6 7 Tensile LD 19,41520,407 TD 19,296 16,990 Elongation LD 63 62 TD 71 77 Ball Burst 12 11OTR 3.0 4.5

TABLE 13 Example 17 Example 23 Example 24 Modulus LD 398,000 420,000437,000 TD 442,000 473,000 488,000 Free Shrink at 220° F.: LD 15 14 15TD 19 19 22 at 240° F.: LD 20 19 19 TD 26 26 28 at 260° F.: LD 30 30 26TD 38 36 38 at 280° F.: LD 44 44 44 TD 51 51 52 at 300° F.: LD 64 63 62TD 68 67 68 Haze Unshrunk 1.8 2.0 1.2 Clarity Unshrunk 82 81 81 Gloss 8683 89 Film Thickness (mils) (related to MVTR data given below) Unshrunk0.89 0.91 0.82 MVTR 2 Unshrunk 0.33 0.36 0.33 Corrected 0.39 0.44 0.36for 75 gauge Tear LD 1 7 4 TD 5 7 6 Tensile LD 28,000 31,000 28,000 TD29,000 33,000 29,000 Elongation LD 80 86 84 TD 71 52 73

In a typical working example of making the film of the presentinvention:

An ethylene propylene copolymer (Fina 8473) containing about 4% byweight ethylene, was blended with the polypropylene in a blend ratio orabout 92% by weight EPC and 8% by weight PP. (The PP percentage includesthe additives discussed above).

The EPC/PP blend was then blended with a hydrocarbon resin (Regalrez1128 from Hercules) in a blend ratio of about 90% by weight EPC/PP and10% by weight HC.

A second blend was also prepared, in a blend ratio of about 84.5% byweight PP (Exxon PD 4062 E7), 15% by weight HC (Regalrez 1128), and 0.5%white mineral oil (Kaydol from Witco Chemical).

A circular coextrusion die was fed with three extruders to prepare afive layer shrink film. One extruder was used to feed the blend of EPCor polypropylene, and HC, as a melt to the extrusion die to form theouter layers. Another extruder fed a polypropylene (Exxon PD 4062 E7) tothe extrusion die to provide the intermediate layers in the multi-layerfilm. The third extruder provided the second blend of PP and HC to theextrusion die.

The extruded tape was rapidly cooled to room temperature and collapsedby pinch rolls. The tape was subsequently heated to an orientationtemperature. Using a bubble technique well known in the art, internalair pressure stretched the tape to about 4.5 times its unstretcheddimensions in the longitudinal (machine) direction and about 4.0 timesits unstretched dimensions in the transverse direction to form a bubblewhich provided biaxial orientation to the resulting film. The bubble wasthen rapidly cooled by chilled air in order to maintain the orientedstate of the film. Finally, the bubble was collapsed and the expandedfilm gathered on a take-up roll. After orientation, the total wallthickness of the film was about one mil with 50% of the structure beingthe blend of ethylene propylene copolymer and polypropylene; 15% of thestructure being the intermediate layers; and the remainder or 35% of thestructure being the core layer.

It will be clear to one skilled in the arc that the degree of stretchingmay be varied to obtain the desired degree of film gauge or thicknessand to regulate the desired amount of shrink tension, free shrink, andother shrink properties of the final film, depending on the packagingapplication. Preferred stretching or racking ratios are between about3.0 and 8.0 in both the machine and transverse directions.

The multi-layer film of the present invention is preferably notirradiated. However, the sealant material, if extrusion laminated,extrusion coated, or conventionally laminated to the substrate moisturebarrier film, can itself be irradiated or electronically or chemicallycrosslinked prior to lamination. Irradiation ray be accomplished bymeans well known in the art.

The blend ratios of the EPC and PP may be varied according to desiredproperties or end-use of the multi-layer film. For example, increasingthe polypropylene in the blend will add stiffness to the film, but alsoincrease the sealing temperature of the film. Conversely, increasing theEPC in the blend tends to lower the shrink temperature of the orientedfilm, or to increase shrink at the same temperature, and also lowers thesealing temperature of the film. A preferred blend includes betweenabout 4% and 15% PP and between about 96% and 85% EPC.

The multilayer film of the present invention is preferably orientedeither monoaxially or biaxially, and preferably used as a shrink film.Optionally, the oriented film may be further processed by reheating thefilm to a temperature near its orientation temperature, i.e. eithersomewhat below, at, or somewhat about its orientation temperature, toheat set the film. This future processing stem has the advantage ofsubstantially retaining many of the favorable physical characteristicsof an oriented film, such as higher tensile strength, modulus andimproved optical properties, while providing a substantial shrink-freefilm in applications where a shrink feature is undesirable.

The film of the present invention can utilize hydrocarbon resin in atleast one or more, or even all the layers of the film, as long as the HCresin in any given layer is compatible from a process and performancepoint of view with the resin with which it is blended.

Films in accordance with this invention are preferably oriented, andpreferably heat shrinkable. Preferred films exhibit a free shrink at240° F. of at least 10% (LD) and 15% (TD), more preferably at least 15%(LD) and 22% (TD).

Obvious modifications to the invention as described may be made by oneskilled in the art without departing from the spirit and scope of theclaims as presented below.

What is claimed is:
 1. A thermoplastic multi-layer film comprising: a) acore layer comprising an oxygen barrier material; b) two intermediatelayers, on opposite surfaces of the core layer, comprising a polymericadhesive; c) two outer layers comprising a blend of propylene polymer orcopolymer, and a hydrocarbon resin, wherein the hydrocarbon resincomprises a thermoplastic resin of low molecular weight made fromrelatively impure monomers that are derived from coal-tar fractions orpetroleum distillates; and d) a polymeric sealant layer adhered to atleast one of the outer layers; wherein the film is heat shrinkable. 2.The film of claim 1 wherein the oxygen barrier layer comprises apolymeric material selected from the group consisting of: i) ethylenevinyl alcohol copolymer, ii) vinylidene chloride copolymer, iii)polyester, and iv) polyamide.
 3. The film of claim 1 wherein the sealantlayer comprises a polymeric material selected from the group consistingof: i) propylene polymer, ii) propylene copolymer, iii) ethylene alphaolefin copolymer, iv) ionomer, v) polybutene, and vi) blends thereof.